A LAN and an ATM transfer information in different formats. A LAN transmits information in a broadcast style, where each workstation on the LAN is theoretically capable of receiving all information. Each individual workstation only accepts information which is designated for that workstation and ignores all other information.
An ATM system or network creates a point-to-point link between two workstations which wish to communicate with each other. This point-to-point link is established for each communication session, and after the communication session is finished, the configuration used to set up the point-to-point link is eliminated.
A conversion is therefore needed between a LAN and an ATM. Information from the LAN which is to be sent to the ATM, requires a translation of LAN data format and processing instructions into ATM data format and processing instructions. Correspondingly, information from the ATM which is to be sent to the LAN, requires a translation of ATM data format and instructions into LAN data format and instructions. These translations can include modifying the header portion of the information for the respective network, and modifying the operation of the respective network.
Packets of information transmitted over a LAN usually have variable packet lengths. In an ATM network, the information is transferred in cells which have a fixed length. Even if each packet in a LAN was set to a fixed length, the fixed length could be different from the cell length. Therefore conversion is necessary to place the information from packets having variable lengths, into cells having fixed lengths.